不对称三相负载作星形连接，为保证相电压对称，必须有中性线。（    ）

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SQL Error: select id,body,options from ***_enewstiku_ where sourceid='68474' and id < 4421123 and id<>'4421123' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku_ where sourceid='68474' and id > 4421123 and id<>'4421123' order by id asc limit 5